Protective device for multiphase motors



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P. SUTER PROTECTIVE DEVICE FOR MULTIFHASE MOTORS Filed Dec Sept. 8,1931.

V cit Patented Sept. 8, 1931 .UNITED STATES PATENT OFFICE PHILIP]?SUTER, OF BADEN, SWITZERLAND, ASSIGNOR TO AKTIENGESELLSCHAFT 1T3 BROWNBOVERI & CIE., F BADEN, SWITZERLAND, A JOINT STOCK COMPANY OFSWITZERLAND This invention relates toimprovements in protective devicesfor multi-phase motors.

, Electrical'ci'rcuits containing multi-phase motors must be protectedfrom failure of any g phase to prevent overloading of the motor whichwould result in unsymmetrical conditions in the circuit. Such conditionis especially undesirable in synchronous motors as will be clearlyapparent.-

19 Failure of-any one phase may be made to operate the motor switch toswitch the motor off by inserting double armature electro-magnets in thephase of the network. Such electro-magnet armatures are arranged to be3.5 freely movable between contacts connected in conducting relation inthe'relay operated motor switch circuit so that failure of one phasewill allow one end of a double armature to drop thereby closing themotor switch relay circuit. Such relay must, however, be supplied with adamping or retarding device to prevent operation of the switch uponoccurrence of a momentary overload or whenever the motor is connected.

The present inventiomas one of its objects, proposes'to avoid the abovementioned difficulty. of prematureopening of the motor switchr Anotherobject of the present invention is 1 9 to provide structure which willavoid the necessity for a damping or retarding devlce in connection withthe motor switch relay.

.Other objects and advantages will be ap parent from the followingdescription in connection with the drawings wherein;

- V Figure 1 is a diagrammatic view of a multiphase motor protectivecircuit;

Fig.2 is a view similar to that shown in Fig. '1 but illustrating amodification of the invention in elevation;

' Fig. 3 is a top plan view of a portion of the structure shown inelevation in Fig. 2;

and Fig. 4 is an enlarged perspective View of a portion of theinvention.

Referring more particularly to Fig. 1 of the drawings, 5 indicates apolyphase motor supplied with electric current from a circuit havin thephases I, II, III, which are interruptable by a motor switch 6 operableby ac- Application filed December 1, 1928, Serial No.

PROTECTIVE DEVICE, FOR MULTIPHASE MOTORS 323,029, and in GermanyDecember 2, 1927.

tion of a relay 7 on a latch 8 normally holding the switch 6 in closedposition.

Considering the portions of line phase I, it will be seen that aswitching member is con nected into the line immediately behind themotor switch 6 and comprises a resilient bimetallic member or spring 9which is joined to a substantially T shaped portion of insulation 11.The insulation 11 is connected by flexible leads 12 to a secondbi-metallic spring 13 which is secured to a T shaped portion ofinsulation 14, similar to the insulation 11. The member 16 is a flexibleconnection similar to the lead 12, which are for the purpose ofpermitting free movement of the insulators 11 and 14. One portion 17 ofthe circuit of the relay 7 is connected to the line phase I.

Considering the line phase II, a bi-metallic spring 18 is secured to theinsulation member 14 which is provided with a flexible lead 19 and linephase III includes a bi-metallic member or spring 21 attached to theinsulator 11 and connected by a flexible connection 22 to the remainderof the system. It will be seen that the bi-metallic members 9, 21 and13, 18 are connected in across-wise manner in pairs to the insulators 11and 14 respectively and that springs 9 and 13 constitute a portion ofline phase I while springs 18 and 21 are in series in line phases II andIII respectively.

The circuit to the coil of the zero voltage magnet or relay 7 is formedin part by a lead 17 connected to line phase I and the remainder of thecircuit comprises a line 23 connecting line phase II with one of a pairof resilient contacts 24; which are arranged in such relation that theymay be bridged by a contact plate 26 secured to the leg of the T shapedinsulator 14.. A lead'28 connects the contacts 2 1 with one of a pair ofresilient contacts 29 which are joined to lead 17 by a connection 31 tocomplete the'relay circuit. A stop 27, the purpose of which will appearhereinafter is fixed directly above the insulator 14. The contacts 29are adapted to be bridged by a contact plate 32, similar to plate 26 andarranged in a similar relation thereto.

A stop 33 is arranged adjacent to contacts 29 and plate 32 for limitingthe movement thereof.

The full line positions of the several portions of the system show thepositions taken by the'motor switch 6 and the contacts 24 and 29 whencurrent is flowing through all three phases, while the dotted linepositions show the condition of the circuit when the phases arewithoutcurrent. The latter position of the switches is produced by theaction of one of the bi-metallic members when the phase containing thesame is without current. The time constant of the springs is made sosmall that the windings will be protected from damage.

Instead of using two bi-metallic strips 9 and 13 in line phase I, asingle strip 34 may be used as is shown in Fig. 2, in which strips 36and 37 are connected in line phases II and III respectively. Thebi-metallic members 34, 36 and 37 are attached to a commonthreeleggedswitch member or spider 38 having a switch portion 39connected thereto. The switch member 39 has a plurality of contactplates 41,42, 43 and 44, joined in conducting relation, on whichresilient contacts 46, 47, 48 and 49 are arranged in sliding relation.The degree of movement of the contacts 46, 47 48 and 49 is limited by astop member 51 which also aids in breaking contact between the plates orcontacts upon tilting of the s ider.

The circuit of relay 7 includes a lead 17 connected to line phase I, tothe relay coil, a lead 31 from the relay coil to contact 49, contacts 48and 47 and contact 46 to line phase II. It will be understood thatconnection is made between contacts 49, 48, 47 and 46 through contactplates 43, 41, 42 and 44 which are connected in conducting relation.

The positions of the several members shown in Fig. 2 indicates thecircuit in closed condition, that is, all the phases are carryingcurrent. WVhen the switch is opened all the springs 34, 36, 37 willstraighten out equally and member 38 will be moved upwardly without anyrotation, The sliding. contacts 46, 47, 48 and 49 will slide upon thecontact plates 44,42, 41 and 43 respectively whereby connectiontherebetween is broken. However, if a single phase is not supplied withcurrent, the switch member 38 to which the bi-metallic springs 34, 36and 37 are connected will be caused to assume an inclined positiondue tothe fact that two of the springswill be under the influence of currentpassing through the respective phases while the other spring will 'bewithout such influence and, accordingly, will tend to straighten. Suchtilting of the spider 38 will cause breaking of the contact between thesliding rods and the contacting plates carried by the switch member. The

circuit to therelay '7 will accordingly be 5 motor switch.

claims.

The invention claimed is:

1. In a thermal relay for a circuit having a plurality of phases, a relacircuit and a control device therefor, and i-metallic elements in serieswith two of said phases respectively for operating said device when anelectrical condition in one of said two phases differs from anelectrical condition in the other of said two phases and for preventingthe operation of said device when said electrical condition changes tothe same degree in each of said two phases.

2. In a thermal relay for a circuit having a .5 plurality of phases, arelay circuit and a control device therefor, and bi-metallic elements inseries with two of said phases respectively for operating said devicewhen the magnitude of the current in one of said two phases differs fromthat of the current in the other of said two phases and for preventinthe operation of said device when the magnltude of the current in eachof said two phases changes to the same degree. T

3. In a thermal relay for a circuit having a plurality of phases, arelay circuit and a control device therefor, and bi-metallic elements inseries with two of said phases respectively for operating said device toopen 1 said relay circuit when the magnitude of the current in one ofsaid two phases differs from that of the current in the other of saidtwo phases and for operatingsaid device to maintain said relay circuitclosed by said device when the magnitude of the current in each of saidtwo phases changes to the same degree.

. 4. In a thermal relay for acircuit having a plurality of phases,a'relay circuit and control means therefor, said means comprisingcontact elements connected to said relay cin cuit, a tilting memberhaving a contact member cooperating with said contact elements, andbi-metallic elements connected to said tilting member, said bi-metallicelements being responsive to changes of current to different degrees indifferent phases to open said relay circuit and responsive to changes ofcurrent to the same degree in difl'erent phases to maintain said circuitclosed.

In testimony whereof I have hereunto subscribed my name this 14th day ofNovember PHILIPP SUTER.

